Low Surface Brightness (LSB) Galaxies have central surface
 brightnesses in the B which are up to five magnitudes/sq. asec.
 fainter than those of `normal' High Surface Brightness (HSB)
 galaxies (typically B(0) 21.65 mag/sq. asec.). Nevertheless, they
 have relatively normal integrated luminosity and high mass to light
 (M/L) ratios because they are rich in H1 relative to their
 low surface brightnesses. In fact they have more-or-less normal
 total masses. They occur in all Hubble types but are anomalously
 blue. Some LSBs (e.g. large LSB spirals similar to Malin I) may
 harbour AGNs. Historically, selection effects have tended to
 discriminate against the inclusion of LSBGs in galaxy catalogues,
 yet they may in fact constitute a significant component of the
 overall galaxy population. They seem to occur in regions of lower
 galaxy density in which they may evolve slowly and quiescently
 over a Hubble time, without being disturbed by intractions with
 other systems. They constitute a population of objects which is
 novel and distinct from the historically familiar galaxy population
 and yet at the same time entirely significant to the understanding
 of galaxy formation and evolution in general. They present a
 wholely unfamiliar context for star formation, which they support
 almost completely in a H1 medium devoid of molecular gas.

 We propose to extend coverage of these systems into the FIR (out
 to 160 microns) using ISOPHOT. This will greatly extend the
 information that is available concerning the physical conditions
 and environment which govern the highly anomalous star formation
 occurring in these systems. In so doing, we will not just fill a
 gap in the coverage of normal galaxy types with ISO, but rather
 will extend the ISO coverage into a new domain of galaxy
 properties.